At this point in 1992, Clinton's opponents had convinced the public that Clinton was a draft dodger and a philanderer. Clinton's "I never inhaled" was standard material for late-night comics. The word "Clintonian" had become a part of the national vocabulary for making a misleading but factually true statement. And the Whitewater "scandal" was already all over the media, which would eventually result in the appointment of Kenneth Starr as an Independent Counsel.
At this point in 2000, Gore's opponents had convinced the public that Gore had problems with exaggerations and truthfulness. The accusation that Gore had claimed to have invented the Internet was standard material for late-night comics. And the Buddhist Temple "scandal" was already all over the media and may have eventually resulted in the appointment of an Independent Counsel.
So far, Kerry's opponents have made four major attacks against Kerry - that Kerry is a flip-flopper, that Kerry is "too liberal", that Kerry didn't deserve his medals and that Kerry accused his fellow vets of committing atrocities. The "flip-flopper" and "too liberal" attacks have wilted due to Kerry's rock-solid performance in the debates. The "didn't deserve his medals" attack has melted in the face of massive amounts of evidence supporting that Kerry is indeed a war hero. I don't think the last attack is sticking because (1) it is easy to disprove and (2) people know that atrocities did occur in Vietnam. Drudge's "Kerry had an affair with a reporter" attack was such a massive flop that it should provide Kerry some protection on that front. Nothing Kerry has said has become fodder for late-night comics. There have been no "scandal" charges made against Kerry.
If Kerry becomes President, expect the "flip-flopper" and "too liberal" attacks to continue. The "flip-flopper" charge will be an annoying one because whenever Kerry compromises to get legislation passed, you are going to hear the Republicans and the conservative media repeating it. The "too liberal" attack will be easy to beat back by saying, "Is reducing the federal deficit too liberal? Is reducing the cost of medical insurance too liberal? etc, etc."
The one attack that Kerry is really vulnerable to is if another terrorist attack occurs against the US. There hasn't been any terrorist attacks since 9/11, so if one of our buildings or warships get bombed, the Republicans will say that Bush was far better in keeping America safe. As long as that doesn't happen, Kerry may actually have it easy. Because the Republicans never criticized Bush for making a total mess of everything, if Kerry just stabilizes things then it will be hard for the Republicans to criticize him. Also, with Clinton, the Republicans claimed credit for all of Clinton's accomplishments, saying they were the ones who actually forced through the policies that improved the deficit, made the economy boom, etc. They aren't going to be able to do that Kerry as (1) the Republicans had virtually no successes while controlling the House, Senate and White House and (2) hopefully the Democrats will control the Senate, so the Republicans will have even less effect on the government.
The one thing I STRONGLY recommend that Kerry and the Democrats do (assuming that Kerry wins and the Democrats retake control of the Senate) is to give the Bush Administration the thorough investigation that it was never given and send as many people possible to jail. Hold hears in the Plame case, make it clear how badly it hurt the country's intelligence efforts and throw the people responsible for the leak into jail. Find out who got rich off the missing billions in Iraq and throw the scammers into jail. Etc, etc. Bush pushed himself up initially by pushing down Clinton. Given that the entire Republican leadership groveled at Bush's feet, revealing the corruption of his administration will devastate the Republican party.